Just a quick work "Your Lordship" - would be careful about the mileage that you are doing, I think that you are possibly doing too much. When I started running 2 yrs ago, I was doing the same mileage as you, and in the same way. My plantar fascia injury was caused by my increasing my weekly mileage too quickly and I think that you may need to allow more time for recovery between each run. I'm now following a training plan, run, cross train, rest, run, cross train, run,rest. (I per day of the week). The runs are 1)gentle run 2)form run (ie mix of techniques to build speed) and 3) long run (endurance and stamina). It has helped me and it is intended for those returning to running post injury, so perhaps once you're back and running it might be worth consideration. I;ve also just started Pilates to strenghen core muscle groups and funnily enough, my class is full of runners.
Hope you do recover and if you want any more info, post a thread and I'll reply. BTW book is by John Bingham, "Marathon running for mortals" ( from memory).
Good luck